Chitosan-polyvinyl pyrrolidone hydrogel does not activate macrophages: potentials for transplantation applications

We have shown previously that chitosan-polyvinyl pyrrolidone (PVP) hydrogels are blood compatible, islet compatible, and noncytotoxic to various cell types. Because of these potential applications of chitosan-PVP hydrogel, the present study was designed to investigate its effect on macrophage activation. Macrophages did not adhere to hydrogel in culture but maintained their viability and did not undergo apoptosis as confirmed by trypan blue staining and absence of DNA ladder. Hydrogel leach-out products did not exhibit cytotoxic effects on macrophage functionality at mitochondrial and lysosomal level as confirmed by tetrazolium reduction (MTT) and neutral red uptake (NRU) assay. On exposure to hydrogels, macrophages showed comparable expression of activation markers such as CDllb/CD18 (Mac-1), CD45, and CD14 to those cultured in the presence of PTFE, a known biocompatible control, indicating its nonactivating nature. Macrophage activation was also assessed by checking the level of messenger RNA of inflammatory cytokines such as IL-6 and TNF-alpha by reverse transcriptase polymerase chain reaction (RT-PCR), which did not show stastistically significant difference (p > 0.05) in the expression of these transcripts in both control and hydrogel-exposed macrophages. The nonimmunogenic nature of the hydrogel was further confirmed by the lack of induced proliferation of mouse splenic lymphocytes after exposure to hydrogel leach-outs. All these results point out that chitosan-PVP hydrogel did not activate macrophages and thus is immunocompatible. Our results indicate that this hydrogel could be a potential candidate for transplantation studies by virtue of its biocompatibility and imunocompatibility.